Skid indicator for aircraft



May 11, 1948. R. ALKAN ET AL 'SKID' INDICATOR FOR AIRCRAFT Filed Feb. 5, 1945 -21 Sheets-Sheet l INVENTORS [Robert Alkan August R sl "ATTo/g/vgY Ma 11,1948. R. ALKAN ETAL i 2,441,306

SKID INDICATOR FOR AIRCRAFT Filed Feb. 5, 1945 2 Sheets-Sheet 2 4 TTO/ENEY Patented May 11, 19 8 NlYJassign'orsto s eeianiegine. eimlie i en February 5, i i'iel 5 6,25? 7 7 9 tor an object to Fig. 6 is a side viewof a conventional yawatorffor'aircraft. head used with the indicator. Z'is a sectional view" taken on the line 1-7 5 "In the selected embodiment shown in the drawings'forthe'pur'poses' of illustrating the principles of the invention a cyiir'idricalskidindicatingtell tale ele n ent t'i is n ount'ediii asuitabl'esupporting casin in tnefieidrtisieg oi the p'ilo't'to'indicate 10 by its mama "one direction or the other the direction of skid" of" the" aircraft and by its speed Of rotation the ifelatiy bedbf skid. This tell tale is rotated by a vanetype air motor 6, the

ated" on accurate controlio'f" airplane and guns and if he 'is 'toi nairitain anawa feness vanes of iirrichareeiigaged"by a, current ofa'iiof lateral skid, it is important that he should from one or the other of two" forwardly presented have a skid 'indi tor"hichdo'esflnot require dynamic pressure airtube's '8 and awhich are more thaha ni dfatt ention his mounted in fisfibstant'ialiy horizontal plane in observations. theairei'aft andare directed rn'ore or'less laterally The present invention aims to provide a skid inbpposite" directions' fi'omthenornial direction indicator which is easily observed py jihe pilot 2 0 of flight' d'fthdaircraftfl As indicated inFigJ'I,

While reguiring Hi num ofdistractiofi of his thesedynainid pressure tubes are formed in one att tio'n iro ri his arid target". Itis rurinteg'ral yaw and extend forwardly and outnto provide a skid w ny-at ai angl'e'pf'aboutd degreestdthe e rvable' forthe flight axis. *Dynaihie'pressur'e tubes are indicated and described eshneot'theknown'meansfoi' obtaining an air current for the purposes indicated but obviously other ni'eans'for'accomplish- H ing'th'e sah'ieipurposen'iaybe'substitutedf'when, 4 spo'ri'sto due to skid" cr'yaw', the'movemcnt of theplane ctiori 0r 'spe edo skid a'fidi 'vhic'h is diagonal to the normal line of flight, then one wherithe p p 'd' of rotation meet the other will receivea higher'pre'ss'ure N {W I I bl u r an rn al 'ge r dof air and conseque'ntiya' current of air wiil flow ing f trieinlsftrunient fiiciil t. throughbne' of the tubes 8"or 9"and the connect- The nature andobjects of the invention tvili be conduits "into the'chamber'ifi of the'c'a'sing fro rn a description of an iihisand'ageinst the vanes "ito causer otationof the 't ithereoi ",iofth? pur of motor and thesi iici indicator element 5 to which of encesh uldbe'ha the motor rotor is rigidly attached. It is to be noted that in the pref rr d construction illus- H f d h draw n th f e l ale f'rb' 'ete 0 Figure ,1 is a frontview gf a skid indicator aptinuous lyiri one je'ctiono the other indipiied t a s h as viewed bribe ilot ind catin in skid n one Id rec' i o er thereb also dia rammat ca t e air t b c nnect o s iving the pi n n cat n by th a pa to the yaw-head. Y right and left movement of the lines." This provThe sight is indicated in dot and dash lines to vides a difierent typ'e' of indicator than those show the relative position of the"skidindicat'or shown in various devices of the prior art which visible through the sight 'glass'. indicate skid by theirposition as contrasted with Fig". 2 is" a siectioriailviewof the indicator unit a; continuing movement. ,Theterrns rc tate and drawn to a larger 'sc'ale'; rotation as used in the claims'are intended to Fig.1 315a sctioriaiview taken on the line 33 define this type of continuing movement and to ofj igl'zl' distinguish from a mere swinging about a pivot. Fig; 41s a central sectional View taken on the Itis' to'bnot'ed that the air pressures of the two linejfigfi "of T1? 7 dynamic pressure tubes'act' in' opposition'to each Fi'gf s'is afdt iled sectiona l view taken on the othenagainstopposite sidesof .th'e' vanes. The X of: air current may flow forward'in the tubeof lesser pressure if desired or other provision may be made for the escape of the air.

The telltale is suitably marked for visual observation by the pilot. A helical marking in black and white has been found convenient and effective. Such marking gives the appearance of parallel lines visible to the pilot moving to the right or left as the pilot sees the indicator within his field of vision while looking through the sight. The White line may be luminous if desired in order to be visible in the dark.

The casing for the telltale comprises a tubular member l2 having a window l3 and a recessed head member Id providing a motor housing [5 which receives and is spun over the flange l6 of the tubular member as indicated at IT, together with a transparent plastic tube [8 fitting the member 12. The window portion of the plastic tube may be flat to avoid reflections or of lens shape to magnify in one direction the telltale marking.

The motor 6 comprises a disc 20 of aluminum or other nonmagnetic material of good electrical conductivity, rigidly secured to the end of the telltale 5 and having edge portions twisted and formed to provide the vanes 1.

In order to provide damping means to inhibit overrunning and high speed rotation of the rotatable member including the telltale and rotor disk 25, a permanent magnet 21 is fixed in the casing member Hi with north and south pole portions 22 and 23 closely adjacent the disc 20. Preferably also an annular armature 24 is fixed in the casing close to the opposite face of the disc 20. Between their opposed faces the disc 20 of the vane motor rotates. At low speeds of rotation the magnetic lines of force between the permanent magnet 2i and the armature 24 have less damping effect but as the speed increases toward the point at which the rapid rotation would cause blurring, the damping effect becomes very effective. The telltale responds quickly to any reduction of pressure or reversal of flow of the air current partly because of the magnetic damping and partly because the vanes are relatively large as compared to the mass of the rotor.

The shaft 25 of the rotatable telltale element 5 is mounted in jewel bearings 26, 27 for free rotation.

The magnet comprises four permanently magnetized bars 28 two of which are positioned with north ends 22 toward the rotor and two of which are positioned with their south ends 23 toward the rotor. A soft iron cap 29 acts as a retainer for the magnet bars and completes the magnetic circuit.

The skid indicator unit fits in a bracket 30 in which it is held by clamp bolts 3!. The bracket 39 is arranged to be secured to the rear of a sight unit to hold the indicator suitably within the range of vision of the pilot while interfering very little with his field of view through the sight.

The yaw-head is shown in Figs. 6 and '7. As shown it comprises a streamlined head 33 having the two dynamic pressure tubes 3 and 9 formed therein and connecting respectively with passageways 34 and 35 to which suitable conduits 36 and 31 are connected to lead the air currents to the vane type motor. The dynamic pressure tubes are shown as slots having a substantial length longitudinally of the yaw-head to permit air currents of substantial volume while at the same time, the width of the tube is narrow circumferentially of the yaw-head.

The yaw-head is formed with a flange 38 for attachment to the wing of the airplane or other suitable support. The flange is formed with a round hole 39 for a securing screw serving as a pivotal point of support and with two screw slots 40 and 4| arranged concentric with the point of pivotal support to permit adjustment.

The instrument so far described is sensitive to yaw of a fraction of a degree and for satisfactory operation, it is necessary that the yaw-head providing the two dynamic pressure tubes be set parallel to the effective line of flight of the aircraft with corresponding accuracy. In order to overcome the diiiiculties involved in accurately positioning the yaw-head on the aircraft, means is provided for modifying the effect of the current of air coming from one of the pressure tubes until, when flying the aircraft in a straight line with as little yaw as possible, the skid indicator will either stand still or oscillate equally in opposite directions. Rather than restrict one air passage, an arrangement is preferred in which air is bled from one air passage or the other as may be necessary to obtain a zero indication when the aircraft is flying in a straight line in still air.

As shown in Fig, 5, a small cross-passage 43 between the two passages 36 and 45 and a threeway valve 45 provided for releasing air coming from one .or the other of the tubes at and 45. In order to set the valve 48 at the proper zero position to provide a neutral indication by the skid indicator, the craft is flown by the pilot in as straight a line as possible in still air and the valve is set by means of the handle 4'! to provide zero indication.

The foregoing particular description of a selected embodiment is illustrative merely and is not intended as defining the limits of the invention.

We claim:

1. A skid indicator for aircraft comprising in combination, a tubular casing having a window in one side, a rotatable cylindrical member having a helical surface exposed to view through said window, means for rotating said cylindrical member in one direction or the other comprising an electrically conducting disc havin vanes formed at its outer periphery secured to said rotatable cylindrical member, a magnet and an armature fixed in said casing and between which the disc rotates, means including a yaw-head aligned in the direction of normal flight of the aircraft and arranged to lead air currents against said vanes to rotate the rotatable element in one direction or the other.

2. A skid indicator for aircraft comprising a rotatable telltale element adapted to indicate by continuing rotation the direction of lateral skid, an air motor connected to rotate the telltale element, a pair of pressure tubes directed somewhat laterally to opposite sides of the normal direction of flight and means leading a current of air from said tubes to themotor to control its direction of rotation and means for modifying the effect of the air current coming from one tube to provide a zero reading.

3. A skid indicator for aircraft comprising a rotatable telltale element adapted to indicate by continuing rotation the direction of lateral skid, an air motor connected to rotate the telltale element, a pair of pressure tubes directed somewhat laterally to opposite sides of the normal direction of flight and means leading air from the pressure tubes to the motor to rotate it in either direction and means for modifying the effective pressure at the motor of air coming from one of the pressure tubes in order to make correction for errors of alignment.

4. A skid indicator for aircraft comprising, in combination, a telltale adapted to be positioned in the field of vision of a pilot, an air motor connected to said telltale, a yaw-head having a pair .of tubes adapted to lead air to said motor in one direction or the other in accordance with the direction of skid to actuate the motor, and means yieldably inhibiting the movement of the telltale and a valve adapted to bleed more or less air from one Of the tubes to adjust the indicator.

5. A skid indicator for air aircraft comprising, in combination, a rotatable telltale adapted to be positioned in the field of vision of a pilot and to indicate by continuing rotation the direction and extent of lateral skid, an air motor connected to said telltale, a yaw-head having a pair of tubes arranged to lead air to said motor to actuate the motor in one direction or the other in accordance with the direction of skid, means yieldably inhibiting the movement of the telltale, and a cross conduit and valve to control escape of air from one or the other of the tubes.

6. A skid indicator for aircraft comprising a horizontal rotatable helical telltale adapted to be mounted with its axis transverse to the pilots line of sight to indicate, by continuous rotation in either direction, lateral skid of the aircraft, an air motor connected to one end of the telltale to rotate it and a yaw head comprising a pair of pressure tubes leading a current of air to the motor to control its direction and speed of rotation substantially as described.

7. A skid indicator for aircraft comprising in combination a tubular casing having a window in one side, a rotatable cylindrical telltale mounted in the casing and having a helical surface exposed to view through said window, an air motor directly connected to said rotatable telltale for rotating it continuously in one direction or the other, means including a yaw head and conduits arranged to lead air from the yaw head to said air motor to drive it in one direction or the other in accordance with the direction of air flow relative to the yaw head.

8. A skid indicator for aircraft comprising a horizontal rotatable telltale having a. helical surface adapted to indicate by continuous rotation in either direction lateral skid of the aircraft, an air motor connected to one end of the telltale to rotate it and a yaw head comprising a pair of pressure tubes directed somewhat laterally to opposite sides of the normal direction of flight leading a current of air to the motor to control its direction and speed of rotation.

ROBERT ALKAN, AUGUST RASPET.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,298,494 Gwinn Mar. 25, 1919 1,693,211 Weaver Nov. 27, 1928 2,029,700 Boykow Feb. 4, 1936 2,045,521 Hertelendy June 23, 1936 V FOREIGN PATENTS Number Country Date 133,714 Great Britain -Mar. 11, 1921 648,871 Germany Aug. 12, 1987 

